New tempests over the practices of uniformed peace officers have thrust Mayor Bill de Blasio and New York City's two biggest law-enforcement unions into discord.

Tension along these lines is typical for any administration. But the symbolism and politics carry a new flavor as the first Democratic mayor in 20 years deals with a pair of seasoned union leaders who have held office since the 1990s.

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New tempests over the practices of uniformed peace officers have thrust Mayor Bill de Blasio and New York City's two biggest law-enforcement unions into discord.

Tension along these lines is typical for any administration. But the symbolism and politics carry a new flavor as the first Democratic mayor in 20 years deals with a pair of seasoned union leaders who have held office since the 1990s.

Consider first the widely publicized, video-recorded death of Eric Garner in police custody on Staten Island.

Patrolmen's Benevolent Association president Patrick Lynch said the officer who put his arm around Garner's neck, Daniel Pantaleo, is "distraught" over the incident. The PBA's 15-year president, representing 23,000 officers, urged de Blasio to "unequivocally say resisting arrest hurts everyone, police officers and citizens alike, and will not be tolerated," and blasted "police haters."

De Blasio Tuesday expressed general support for the police.

Within the same 24-hour news cycle, Norman Seabrook, who's been president of the New York City Correction Officers Benevolent Association for 19 years, weighed in on U.S. Attorney Preet Bharara's report of a "deep-seated culture of violence" against adolescent inmates on Rikers Island.

With the mayor under pressure to carry out changes, Seabrook, who represents 9,000 officers, said Monday "there may be a few that react with what you might think is excessive force." But he insisted officers, other inmates and property need to be defended.

For perspective: Lynch repeated as a mantra during early scrapes with Mayor Michael Bloomberg, "This mayor just doesn't care."

And there's a more routine potential source of tension: De Blasio, who reached long-delayed contract agreements with the United Federation of Teachers and District Council 37, has yet to do so with COBA or PBA.

Lynch has publicly clashed with the Rev. Al Sharpton over the Garner case and its aftermath, which is unsurprising. But the context is new. Sharpton, for the first time in this kind of police controversy, plays the role of putative City Hall political ally.

At an Office of Emergency Management event in Brooklyn Tuesday, de Blasio fielded questions about the statements from Lynch and Sergeants' Benevolent Association president Edward Mullins hitting back at police critics.

"I've long since learned to listen respectfully to the words of union leaders," the mayor said, but added the presidents "will say what union leaders say. That is historic, that's been going on for decades."

"There's no contradiction between doing your job effectively and respecting the people you serve, and that's very clear in the rules of the NYPD."

While a legal process plays out in the Garner case, de Blasio has 49 days to respond to the Rikers report. New correction Commissioner Joseph Ponte -- who drew early fire from Seabrook -- has carefully said he'd work with federal officials on "appropriate and feasible" remedies.

In this serious arena, you can bet on de Blasio to keep proving even more cautious than usual in his public remarks.